CAD render 3ring construction

Frodo - a 10 inch travel Dobson

10 inch, f/4.8 newtonian


TM logo Telescope Making
Web Ring
Next | Previous | Random | List Sites
Next 5 | Previous 5 | Join





basic considerations


hogging out
smoothing the curve
foucault tester


mirror cell
wire spider
middle ring
rocker box


travel and assembly






I have used Frodo for about 20 observation nights now and taken it on one holiday tour with my family. The low storage volume has been a real plus. It fitted neatly into the trunk of my VW, leaving plenty of space for all the gear, kids toys etc.

The observing has been as comfortable as I hoped it would be. I use any ordinary chair and rotate the OTA so I have a relaxed viewing position. Rotating the OTA could be a bit easier, though. Maybe later I'll equip the two middle rings with formica and teflon, if I can be bothered.

I can switch from focuser left to focuser right in no time. I haven't decided if I'd rather push or pull the scope, yet. For me, both is OK. That way I can, depending on the wind direction, position myself always to a leeward position if I find my body heat flows through the light path. The quickfinder attaches via one thumbscrew and can be moved to either side of the focuser for easy access.

I've had spectacular rich-field views with my 32mm 2inch eyepiece with bearable coma at the fov edges (maybe some day I can afford Uncle Al's hand grenade), but so far, high magnification (beyond 200fold) is not satisfactory and I am troubleshooting at the moment.

The in focus images of bright stars using my Stratus 3.5 mm (340fold) show blurred specs of light. I haven't had a decent Airy disc, yet. The intrafocal and extrafocal images show clearly distinguished diffraction rings that are separated with good contrast by dark rings. Intra- and extrafocal images show little difference. However, the are always on the move, disturbed by turbulence and show radiant beams.

I am not an experienced observer and cannot decide, if it is due to the main mirror, collimation, the secondary (a bargain), mechanical flaws or the seeing.

The foucault pictures and readings don't look too bad and though it is possible I mismeasured, I rather think it is due to misalignment of the homemade focuser and/or position of the secondary (a laser would probably come in handy, here. I will probably re-rig the wire spider with stronger wire, the 0.2 mm I use now are a bit on the thin side.

So my preliminary resumee is: I am pleased with the mechanical performance and the travel ability - the optical performance, I hope, will live up to this as soon as I know what to do, refigure the main mirror, get a better secondary, find a decent climate ...




   © 2005 by Andreas Derwahl •  contact